Originally posted by Transit The tele-adapter will lose light though ?
A rear-mounted TC eats light. A screw-on front adapter doesn't. This is similar to using a Raynox close-up adapter versus macro tubes. The extension eats light, the Raynox doesn't. The cost of using any add-on optics is some slight loss of contrast and saturation, which can be tweaked in PP / RAW development or in-camera. With close-up and wide adapters, and cheap tele adapters, there is also some loss in edge acuity, but I haven't seen that with good tele adapters.
Brands to look for include Sony, Olympus, Canon, Kowa, Quantaray|Sigma, Vivitar, Minolta, Sankyo, Promaster|Tamron, Kenko -- NOT Phoenix, Star-D, Tiffen, no-names. Ambico may be OK but I'm not sure.
Here is where I search for them. Like I said, stick to name brands. Plug in 1.4x or 1.7x as well as 1.5x for searching. Many of these are for camcorders -- avoid those with rear threads under 46mm. I use a Sony VCL-1546A, which means 1.5x on a 46mm thread, and I use it (via step rings) on lenses with 49mm or 52mm threads, with no vignetting. It cost me US$4 shipped. My Kowa 1.75x was one buck less. I have no complaints.